Different approaches for such an antenna with circularly polarized electromagnetic waves having a hemispherical radiation pattern exist. In particular, the global positioning system (GPS) is a global navigation satellite system, which necessitates the use of optimized antennas. GPS satellites broadcast radio signals to enable GPS receivers to determine location and synchronized time. GPS signals include ranging signals, used to measure the distance to the satellite, and navigation messages. The navigation messages include data, used to calculate the position of the satellite in orbit, and information about the time and status of the entire satellite constellation, called the almanac. This information is modulated onto an electromagnetic signal having a predetermined polarization. These antennas have particular requirements that must be met.
For example, a relatively high transmission bandwidth is desirable, such that the antenna can be operated across a large frequency range. Next, the radiation pattern of the antenna should preferably be hemispherical such that signals are received from as many satellites as possible. Finally, a good circular polarization is required across the bandwidth of the antenna. However, other applications for such an antenna are also possible. For example GB 2,198,290 discloses a dual-band circularly polarised antenna with hemispherical coverage. U.S. Pat. No. 7,477,201 discloses a low profile antenna pair system.